a. Field of the Invention
The instant invention relates to catheters. In particular, the instant invention relates to catheters employing shape memory alloy wires as shaping wires and/or pull wires.
b. Background Art
Catheters are used for an ever-growing number of procedures. For example, catheters are used for diagnostic, therapeutic, and ablative procedures, to name just a few examples. Typically, the catheter is manipulated through the patient's vasculature and to the intended site, for example, a site within the patient's heart. The catheter typically carries one or more electrodes, which may be used for ablation, diagnosis, or the like.
To increase the ability to move and navigate a catheter within a patient's body, steerable catheters have been designed. Steerable catheters are often manipulated by selectively tensioning one or more pull wires running along the length of the catheter, typically offset from a central axis of the catheter, thereby deflecting the distal end of the steerable catheter in one or more planes. Steerable catheters may also utilize shaping wires that form the distal end of the catheter into a desired, preset geometry to facilitate proper positioning of the catheter within the patient's body. These pull wires and shaping wires are often attached to a metallic catheter component located at the distal end of the catheter, such as one of the electrodes carried on the distal end of the catheter or a pull ring incorporated in the catheter, through a metallurgical joining process such as silver brazing.
It is sometimes desirable to utilize shape memory alloys, such as nickel-titanium, in pull wires and shaping wires. Shape memory alloy pull wires are desirable in that they facilitate restoring the distal end of the catheter to an undeflected position when the pull wires are unloaded (e.g., not in tension) by tending to return to their undeformed shape. Shape memory alloy shaping wires are desirable in that they permit the catheter to rebound to a preset geometry after deformation, such as application of a straightening device in order to insert the catheter into the patient's body through a relatively small incision.
Since it is difficult to metallurgically join shape memory alloys to other metals, such as those typically employed in catheter electrodes or pull rings, it is known to provide a short stainless steel sleeve, commonly called a crimp sleeve, over the distal end of the shape memory alloy wire. The crimp sleeve is typically mechanically fastened to the distal end of the shape memory alloy wire, and the crimp sleeve is then metallurgically joined to the tip electrode or other metallic catheter component.
As catheters are used in smaller and smaller passages, there is a growing need to use catheters that have a smaller outer dimension. Accordingly, there is a need to use steerable catheters that have smaller cross-sections. The use of a crimp sleeve about the distal end of the shape memory alloy wire, however, increases the outer diameter of the shape memory alloy wire by between about 0.006″ and about 0.010″. This may make it more difficult to manufacture catheters of reduced outside diameter, and may also undesirably restrict the maximum outer diameter of the shape memory alloy wire than can be employed in a catheter having a particular outside diameter.